MadSci Network: Botany
Query:

Re: How to use dead plant material, remove DNA, and insert into new seed

Date: Sun Apr 25 21:27:25 2010
Posted By: Alex Brands, Post-doc/Fellow, Biological ciences, Lehigh University
Area of science: Botany
ID: 1265867505.Bt
Message:

Hi Matt,

It sounds like you are asking about cloning a dead plant by transferring its DNA into a living seed. Iím sure that has never been doneÖall plant cloning to date has used living tissue, and there is no need to involve a seed from another plant (see below)

Animal cloning involves a technique called somatic cell nuclear transfer. Put simply, the nucleus from a somatic cell (ie, not a sperm or egg cell) is taken out and transferred into a donor egg cell that has had its nucleus removed. To date, this process has not been done with plants, probably because there are much easier ways to clone most species of plants, but only when they are alive.

Most plants can be cloned from cuttings, although some are more difficult to clone this way than others. This technique simply involves cutting a branch from a plant and getting that branch to produce roots. In the easiest cases, this can be done just by sticking the cutting in the soil and keeping it moist until roots form. In more difficult cases, the cutting has to be treated with plant hormones to stimulate the formation of roots. Other plants can be cloned by root cuttings. In this case, a section of root is removed, and under the right conditions, it will form shoots and leaves, becoming a complete plant and clone of the original.

In the most difficult cases, a piece of leaf tissue is excised, and cultured in sterile conditions in a Petri dish or test tube. By using the appropriate hormones, researchers can induce the formation of shoots from the tissue. Once they have formed, different hormones are applied to stimulate root formation, and a little plant is formed. This tissue culture technique, while complex, is still far easier than somatic cell nuclear transfer.

The point Iím trying to make is that there is not much incentive to develop somatic cell nuclear transfer cloning technology in plants, because there are much easier ways to clone plants.

If someone was interested in cloning a dead plant, something like somatic cell nuclear transfer might sound like a promising approach, but there are some major obstacles.

The first issue is getting intact DNA from dead tissue. All plants have several long chromosomes of DNA in each cell, and without an active system of repair, it is extremely unlikely that any one cell from dead plant tissue has a complete set of intact chromosomes, unless the tissue was carefully and quickly preserved at very low temperature. Further complicating matters is the fact that there is no way to tell if a single dead cell has a complete set of intact chromosomes. Isolating fragments of DNA is doable, but that would not be of use if the goal is to clone a plant.

However, if you did manage to find a good donor cell, the next step would be to take the nucleus out of a recipient cell, and inject the donor nucleus in. You can see a video of this process in animal cells here: http://www.youtube.com/watch? v=OCro5zfc3uc

Unlike animal cells, plant cells have a rigid cell wall on the outside, so it would be more difficult to get the needle in and out.

In your question, you asked about transferring the DNA into a seed, but this is probably not the way to go. Within a viable seed is a plant embryo that is made of many cells. To get a new plant that has the DNA of the dead plant you are trying to clone, all the cells of the embryo would have to have their nuclei removed, and donor nuclei put in.

Otherwise, the resulting plant would genetically be a mix of the donor and recipient, a.k.a. mosaic. If the embryo was made of 100 cells, and you transformed one of them, only 1% of the resulting plant would be genetically identical to the dead donor plant. Somatic cell nuclear transfer is not easy, and often fails, so the chance of succeeding with even a majority of cells from a plant embryo is, practically speaking, zero.

A more reliable approach would be to use leaf cells as recipients for nuclear transfer, which could then theoretically be propagated by tissue cultureÖit is possible to generate entire plants from single cells. Another possibility would be to transfer the donor nuclei into an unfertilized egg from the flower of the recipient plant, but then the egg would have to be put back into the flower after the procedure, so it could develop into the embryo in the seed. Keep in mind that no cloning like this has ever been done in plants, Iím just exploring the (very) hypothetical possibilities.

So, Iím sorry to disappoint you, but as of right now, itís not possible to clone a dead plant. The closest possibility may be somatic cell nuclear transfer, but this has not been done with plants, nor has it been done using dead animal tissue.

Dr. Alex Brands
Lehigh University


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